The present invention relates to a method of forming the electrode wirings in semiconductor devices. By "electrode wirings" is meant interconnections between semi-conductor devices and electrodes for connection of leads to semiconductor devices. The method of the invention pertains in particular to an improvement of the so-called lift-off method.
The so-called lift-off method of forming the electrode wirings in a fine pattern such as that in highly integrated IC circuits, as shown in FIG. 1, is well known. Referring to FIG. 1, 1 denotes a substrate of silicon, on which a silicon oxide film 2 (hereinafter referred to as a SiO.sub.2 film) is formed.
On top of this film, the electrode wiring is formed by the following process. First, as shown in FIG. 1(a), a photoresist 3 is applied to the SiO.sub.2 film and then, with a photomask 4 closely fitted thereover, an exposure to ultraviolet ray 5 is carried out. Then, the exposed part of the photoresist is removed with a solvent (FIG. 1(b)). On the surface having the photoresist pattern 3a formed as a mask thereon in this way, a vapor-deposition of Al is carried out, to form an Al film 7 covering both the photoresist pattern 3a and the exposed part 6 of the SiO.sub.2 film 2 (FIG. 1(c)). This Al film 7 is thinner than the photoresist pattern 3a, e.g. is less than one-third the thickness thereof. Following this, the photoresist pattern 3a is removed by the use of a photoresist stripping solution. This process is possible because the Al film has a stepped part 8 which is very thin at the boundries between the photoresist pattern 3a and the exposed part 6 of the SiO.sub.2 film. By this process, the Al film 7 is cut off at the stepped part 8, and at the same time, the part of the Al film 7 on the photoresist pattern 3a is removed, and as a result, the electrode wiring is formed by the portions of the Al film pattern 7a left on the SiO.sub.2 film 2.
Since the thin part of the Al film 7 at the stepped part 8 must be provided in order to carry out this method, it is not practical to vapor-deposit the Al film 7 so that it has a great thickness. Thus, the electrode wiring formed by this method is susceptible to wire-breakage which is a hindrance to the improvement in the yield in the production of integrated circuits.